It is common practice in fields and industries that require pulling metal cable or metal rope through space to use a cable gripping mechanism that includes the ability to grip and release the cable on demand, so the cable can be pulled through space. Oftentimes, the pulling apparatuses utilize a pair of gripping mechanisms, one gripping while the other is released so the cable can effectively be pulled “hand over hand.” In these circumstances the gripping mechanisms work in tandem to create a winching mechanism or system for intermittent and continuous heavy pulling, lifting and lowering.
Ideally, the grip and release mechanism is designed to prevent the cable slipping backwards. In addition, the mechanisms typically include a gripper having an inner surface that defines an aperture or axial channel for the cable or wire rope, lined with “teeth” that bite the cable and hold it in position as the gripper is forced down on to the cable. These “teeth” typically are created by means of serrations or threaded ridges on the cable engaging surfaces of the axial channel.
In part because of the great force placed on the cable as it is being pulled (typically, cable pulling machines can have a pulling force of anywhere from about 6 to 100+ tons) the cable can have a tendency to twist as it is pulled, making it difficult to maintain an even grip or pressure on the cable with cable gripping mechanisms in the art. Thus cable gripping mechanisms or systems in the art are subject to great wear and tear, and have a tendency to seize, and/or require the need for anti-seize lubricants to allow them to function properly in the field. Another impact of the great force systems in the art apply to cable or wire rope surfaces is that they “bite” the cable so strongly they tend to cut the individual wire strands, fraying the rope or cable and thereby weakening it.
Many gripper mechanisms typically in use in the art work on a wedge principle where the cable or wire rope is sandwiched between member segments that together define a wedge set. As the wire rope is pulled, each half of the wedge set is forced down onto the cable, squeezing the cable or wire rope, and biting the rope with gripper “teeth”. Often the wedge slides along a tapered surface so that the wedge pieces are forced down onto the cable or wire rope as the wedge moves forward along the taper. Generally, movement occurs due to a force applied to the rear of the wedge, for example mechanically by a spring, or hydraulically. (See, for example, Chant Engineering's “Wire Rope Grips”, http://www.chantengineering.com/wirerope.php?I=1.) See, also US published patent application 2016-0348807-A1. Another wedge gripper is illustrated by the vertical pulling apparatuses of TricTools, Inc., (see http://www.trictools.com/product-category/pulling-units/.) In this system, the wedge segments are forced onto the cable surface by both a slide mechanism and by a series of elastomers that bind the segments to the slide mechanism. Still another system illustrated by Pow-r Mole Sales LLC uses a levering means to translate hydraulic force to a wedge segment in a vertical gripping system. The lever has a central pivot point. As hydraulic force pushes one end of a lever up, the other end of the lever, attached to a wedge segment, is forced down or onto the cable surface. Like the other systems in the art, these wedge segments are acted on independently. In addition, the force translation in the lever system is such that cable gripping can result in cable fraying.
Existing gripper systems often are multi-piece systems that can be complicated or cumbersome to install, especially in a vertical pulling system. One drawback of existing gripper mechanisms is the number and complexity of components to the mechanism that can break in the field, in part due to the high pressure exerted on them, and the difficulty in keeping tension even on the cable from both gripper wedges. The multiplicity of independent components also can make the gripper mechanisms difficult or cumbersome to install, remove or repair, especially in the field. Sliding wedge components can have a tendency to seize and so can require use of anti-seizing compounds, making the grippers difficult to clean. In addition, these systems typically are open systems, and debris can get caught between the gripper wedges and the tapered or sliding surface, making seizing more likely and/or otherwise impeding proper movement of the wedges and even pressure on the wire surface. Cleaning the debris out in the field can be cumbersome at best, and often difficult. Keeping the system in good working condition in open systems typically requires taking the components apart and carefully cleaning out debris and excess grease or lubricant, also a tedious and cumbersome activity.
In systems using large wedge pieces that grip a long length of cable, proper cleaning is especially difficult. Moreover, where the applied force is provided hydraulically, an additional system (the hydraulic system) with its own maintenance and power needs, has to be maintained and managed in the field.
In addition, some gripping mechanisms work only in a vertical or horizontal system, but not both. This can be a drawback in designing pulling or winching systems for multiple applications where it can be advantageous to utilize a range of pulling positions for different operations. It would be advantageous to have a “universal” gripper system that can work in either a vertical or horizontal position without modification. It also would be advantageous for the gripper system to be able to occupy both the “front” and “rear” position without modification, in tandem cable gripper systems where the grippers form part of a “hand over hand” cable winching system with front and back cable grippers alternating gripping the cable.
There remains a need for a wire rope or cable gripper system that provides consistent, timed pressure on both sides of a cable during operation, and can provide that pressure mechanically without requiring an additional system to move it; that can be installed as a unit; that is easy to use and maintain; that has few moving parts; is less subject to wear and tear; that is small and compact; that can be fabricated as a “closed system” such that the force translations means is not impacted by debris in the field; that can be applied in both horizontal and vertical systems; that does not require a sliding surface to support engaging and gripping a wire rope surface, and that is not subject to seizing, even under high pulling forces.
The present disclosure describes improvements in metal cable or rope gripping mechanisms and methods of use thereof that overcome deficiencies in the mechanisms and devices of the prior art.